Referring to FIG. 1, a conventional hermetic compressor is illustrated in sectional view. The hermetic compressor is a device to suction, compress, and discharge a refrigerant under a hermetic atmosphere, and includes a compression unit 10 to compress the refrigerant, and a drive unit 20 to drive the compression unit 10.
The compression unit 10 is arranged in a hermetic container 1 that defines a hermetic space therein. The compression unit 10 includes a frame 11, a cylinder block 12 that is integrally formed with the frame 11 and has a compression chamber 12a defined therein, a piston 13 that reciprocates in the compression chamber 12a, and a cylinder head 14 that is coupled to a side of the cylinder block 12 and has a suction chamber 14a and a discharge chamber 14b, which is open to the outside.
The drive unit 20 includes a stator 21 that produces a magnetic field, a rotor 22 that rotates by electromagnetic interaction with the stator 21, and a rotating shaft 23 press fitted in a hollow portion of the rotor 22 to rotate along with the rotor 22.
An eccentric unit 24 is provided on the top of the rotating shaft 23, and in turn, a bushing 26 is inserted on the eccentric unit 24. The bushing 26 is integrally formed with a connecting rod 28 to connect the rotating shaft 23 with the connecting rod 28, to convert the rotating motion of the rotating shaft 23 into a linear reciprocating motion of the piston 13. The rotating shaft 23 has an oil path 23a defined therein to supply oil to the compression unit 10 and the drive unit 20. When the rotor 22 rotates via interaction with the stator 21 a magnetic field is produced and the oil stored in a bottom region of the hermetic container 1 will be suctioned into the oil path 23a by a centrifugal force generated by rotation of the rotating shaft 23. The suctioned oil is then injected into the compression unit 10 via the eccentric unit 24 provided on the top of the rotating shaft 23.
The eccentric unit 24, having a hollow cylindrical shape, is eccentrically aligned with the rotating shaft 23, so that different centrifugal forces are applied to respective portions of the eccentric unit 24 during rotation of the rotating shaft 23. For example, the largest centrifugal force is applied to a portion 26 of the eccentric unit 24 located at a farthermost distance from a center axis of the rotating shaft 23. Thus, the oil, suctioned through the oil path 23a, is injected along an inner peripheral surface of the eccentric unit 24 in the same direction that the largest centrifugal force is applied. At maximum rotation of the piston 13 as it advances in the compression chamber 12a in accordance with rotation of the rotating shaft 23, the largest centrifugal force is applied to the eccentric unit 24 in a direction toward the piston 13, and thus, the oil from the eccentric unit 24 is injected into the piston 13.
The oil, injected into the piston 13, adheres to an outer peripheral surface of the piston 13, and thus, is introduced into the cylinder block 12. Consequently, a certain interior volume of the cylinder block 12 is occupied by the introduced oil. However, this is problematic because a decreased amount of gaseous refrigerant is introduced into the cylinder block 12 due to the amount of the introduced oil, resulting in degradation of compression capability. Also, the conventional hermetic compressor has no ability to determine an injection direction or injection degree of oil from the eccentric unit 24 of the rotating shaft 23. Thus, a large amount of oil may be injected into a region that requires only a slight amount of oil, or a small amount of oil may be injected into a region that requires a large amount of oil. This results in degradation in operational efficiency of the compressor.